Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

We present a tunnel spectroscopy study of single PbS Quantum Dots (QDs) as function of temperature and gate voltage. Three distinct signatures of strong electron-phonon coupling are observed in the Electron Tunneling Spectrum (ETS) of these QDs. In the shell-filling regime, the $8\times$ degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon sub-bands that result from the emission of optical phonons. At low bias, a gap is observed in the ETS that cannot be closed with the gate voltage, which is a distinguishing feature of the Franck-Condon (FC) blockade. From the data, a Huang-Rhys factor in the range $S\sim 1.7 - 2.5$ is obtained. Finally, in the shell tunneling regime, the optical phonons appear in the inelastic ETS $d^2I/dV^2$.Comment: 5 pages, 5 figure

Statistical flaw strength distributions for glass fibres: Correlation between bundle test and AFM-derived flaw size density functions

cited By 11International audienceThe present paper investigates glass fibre flaw size distributions. Two commercial fibre grades (HP and HD) mainly used in cement-based composite reinforcement were studied. Glass fibre fractography is a difficult and time consuming exercise, and thus is seldom carried out. An approach based on tensile tests on multifilament bundles and examination of the fibre surface by atomic force microscopy (AFM) was used. Bundles of more than 500 single filaments each were tested. Thus a statistically significant database of failure data was built up for the HP and HD glass fibres. Gaussian flaw distributions were derived from the filament tensile strength data or extracted from the AFM images. The two distributions were compared. Defect sizes computed from raw AFM images agreed reasonably well with those derived from tensile strength data. Finally, the pertinence of a Gaussian distribution was discussed. The alternative Pareto distribution provided a fair approximation when dealing with AFM flaw size. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Mesure et cartographie à l’échelle nanométrique des propriétés ferroélectriques et diélectriques des couches minces par les techniques dérivées de la microscopie à force atomique

Cette communication vise à présenter l’apport des techniques dérivées de la microscopie à force atomique en mode contact à la caractérisation des propriétés électriques des couches minces diélectriques et ferroélectriques. La cartographie et la mesure indirecte de la direction de polarisation ferroélectrique sera abordée à travers le mode «Piezoresponse Force Microscopy» dont on montrera les capacités sur un exemple particulier. Nous montrerons également que des mesures capacitives (scanning capacitance microscopy – SCM) peuvent apporter de précieuses informations à l’échelle très locale sur les paramètres essentiels de ces couches minces déposées sur substrat semi-conducteur, comme la présence de charges fixes ou d’interface, ainsi qu’une estimation de la tension de bande plate. Enfin, nous verrons quelques applications de mesures locales de courant de fuite (Conductive AFM) dans les couches minces d’oxydes à haute permittivité. Des exemples seront présentés tirés de la caractérisation de couches minces de LiTaO3 monocristallin, PbZrTiO3, SiO2 ou LaAlO3

Influence of the surrounding ambient on the reliability of the electrical characterization of thin oxide layers using an atomic force microscope

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Structure and morphology of Ge nanowires on Si(001): Importance of the Ge islands on the growth direction and twin formation

International audienceUnderstanding and controlling the structural properties of Ge nanowires are important for their current and future use in technological applications. In this study, the initial stages of the heteroepitaxial growth of Ge nanowires on Si(001) via the Au catalyzed vapor-liquid-solid (VLS) method are investigated. We observe a Ge island located at the base of each nanowire. We propose that these islands are formed by the VLS mechanism and initiate the nanowire growth. Analysis of the islands morphology helps to explain the 〈011〉 growth direction commonly observed for Ge nanowires. Moreover, our observations provide an insight into the formation of twins that propagate along the growth direction

Comparative ageing behaviour of commercial, unworn and worn 3Y-TZP and zirconia-toughened alumina hip joint heads.

There is a trend today to develop zirconia toughened alumina (ZTA) composites for orthopaedic applications. So far, there is limited data concerning their sensitivity to ageing, especially considering tests performed on implants produced on an industrial scale. Here, complementary tools were used to assess the ageing resistance of ZTA femoral heads. The results were compared to femoral heads processed under the same industrial process with monolithic 3Y-TZP. As expected, monolithic 3Y-TZP implants exhibited significant ageing. In contrast ZTA femoral head showed no sign of degradation even over a period equivalent to that of a human life. The potential impact of coupling effects between wear and ageing is assessed. Monolithic zirconia and ZTA femoral heads were thus first worn in a hip joint simulator, and then aged in autoclave. The kinetics of transformation of the worn monolithic zirconia implants is accelerated while that of worn ZTA femoral heads remains almost unchanged

Growth of gold nanowires at the apex of AFM tips

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Phase transformation mechanisms occurring during spark plasma sintering elaboration of new duplex composite stainless steels

International audienceThis study focuses on the elaboration of duplex stainless steels (DSS) from powder mixtures using spark plasma sintering (SPS). Different mass fractions of an austenitic 316L powder and a ferritic 410L one were blended and then sintered by SPS. Microstructural characterizations of the sintered samples obtained from different powder mixtures were performed. They were coupled with marking experiments of the powder particles’ surface. The results showed the formation of martensite within the ferritic powder and at the austenite/ferrite interfaces, following two different mechanisms. In addition, it was found that the width of the martensitic regions is mainly influenced by the diffusion of Cr and Ni from the austenitic to the ferritic powder during sintering. The characterizations revealed that the originality of this approach lies in the particular microstructure obtained after sintering. The characteristic size of the ferritic and austenitic domains in the final material is that of the initial powder particles (up to some hundred microns). Moreover, each domain is formed by equiaxed and isotropic grains, having a size ranging from some microns to some tens of microns. This particular microstructure justifies the use of the term “composite duplex stainless steels” (COMPLEX) for this kind of new DSS